Introduction: the EpiAir (Air pollution and health epidemiological surveillance and prevention) Project has been conducted in 10 Italian cities In this paper we describe the health data used to detect adverse health ejects associated with air pollution exposure (mortality and hospital discharge databases) and to identify comorbidities (based on hospital discharge databases) as susceptibility factors to the effects of air pollution. Material and methods: for each city, we performed descriptive analyses of mortality data included in the study. We considered subjects aged 35+ years old, resident and deceased within the cities in the study period (2001-2005) for non-accidental causes For each deceased subject, information were collected on hospital discharge diagnoses in the previous 2-year period. Urgent hospital admissions of subjects resident in nine cities and hospitalized within the city for specific diseases (including cardiac, cerebrovascular and respiratory conditions) were also included as endpoints Annual mean raw death and hospitalization rates were calculated far each city. Results: 276205 deaths and 701,902 urgent hospital admissions have been included in the study Annual mean crude death rates for non accidental tames in the population aged +35 yrs resident and deceased in the municipalities ranged from 12 1 and 15.7 per 1,000 residents. the percentage of deceased subjects with at least one of the selected comorbidities ranged from 32 to 48% Annual Mean crude urgent hospitalization rates in the resident population ranged from 5 5 to 11 7 per 1,000 residents far cardiac diseases, 1 7 to 3 7 per 1,000 residents for cerebrovascular diseases and 3 3 to 10 7 per 1,000 residents for respiratory diseases. Several factors can explain the between-cities differences observed, especially in the hospitalization rates, including availability and variability in the health care services utilization Conclusion: an epidemiological surveillance system based on health databases has to take into account the observed differences. (Epidemiol Prev 2009, 33(6) suppl 1: 43-50)